A practical reference on cake: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2025-08-19 and is reviewed periodically as new material appears.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen to convert liquid water into ice. Next, the pressure is reduced below the triple point of water so that ice changes directly into vapor without passing through a liquid phase. This step is called primary drying. The result is a porous solid or cake that retains the original shape of the frozen solution.
After primary drying, secondary drying removes water that remains bound to the material. This stage raises the shelf temperature while maintaining low pressure, which encourages desorption of unfrozen water. Residual moisture can be reduced to a low percentage, improving stability for many products. The process parameters, including freezing rate, shelf temperature, and chamber pressure, influence the final pore structure and reconstitution behavior. Control of these variables helps prevent collapse or meltback during drying.
A formulation often contains excipients that protect the active ingredient during freezing and drying. Bulking agents provide structure, while lyoprotectants stabilize sensitive molecules. The freezing step can produce ice crystals whose size and distribution affect the drying rate, and cycle design includes freezing, annealing, and drying phases. If the product temperature rises above a critical value, the cake may collapse or lose its porous structure. Successful lyophilization therefore depends on the interaction between formulation, equipment, and cycle design.
A typical cycle begins with freezing, sometimes including an annealing step to control ice crystal size. Freezing conditions influence the pore network that later allows vapor escape. During primary drying, shelf temperature and chamber pressure are set so heat enters the product while its temperature stays below the collapse or eutectic point. Secondary drying then raises the shelf temperature to desorb bound water and lower residual moisture. Cycle design depends on formulation, fill volume, container type, and equipment capability.
The physics of lyophilization couples heat transfer, mass transfer, and phase behavior. Sublimation requires a vapor pressure difference between the ice front and the chamber, and the dried layer adds resistance to vapor flow. Amorphous formulations are characterized by a glass transition temperature of the maximally freeze-concentrated solute, often denoted Tg'. Crystalline bulking agents can provide structure, while amorphous excipients stabilize labile components. Open questions remain about spatial heterogeneity, edge effects, and how laboratory cycles scale to production.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Freeze-drying, lyophilisation | Lyophilization is the American spelling; lyophilisation is British |
| Primary drying mechanism | Sublimation of ice | Occurs under vacuum below the triple point |
| Typical chamber pressure | 0.05-0.5 mbar | Range depends on product and equipment |
| Typical shelf temperature during freezing | -40 to -20 °C | Lower temperatures may be used for labile products |
| Resulting product form | Porous cake or powder | Appearance depends on formulation and cycle |
Freeze-drying is distinct from simple evaporation and from spray drying. Evaporation removes water at temperatures above freezing, while spray drying rapidly dries droplets in a heated gas stream. Lyophilization avoids high temperatures, which can be useful for heat-sensitive materials such as proteins, vaccines, and some foods. The porous cake produced by sublimation dissolves or rehydrates more quickly than a dense dried mass. Not all materials tolerate freezing or the pH shifts that can occur as solutes concentrate during ice formation.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and fixes the structure of the sample. After freezing, primary drying lowers pressure so ice changes directly to vapor without passing through a liquid phase. Secondary drying then removes bound water that remains after ice sublimation. The result is a dry, porous solid that often retains its original shape.
The low pressure used during drying allows water vapor to move from the ice surface to a cold condenser. Energy supplied as heat drives sublimation but must stay below the collapse temperature of the frozen matrix. If the product becomes too warm, the frozen structure may soften or melt, reducing pore formation and slowing drying. Formulations often include bulking agents, stabilizers, or buffers to support a rigid cake. The final moisture content depends on formulation, freezing rate, and the length of secondary drying.
The physics of freeze-drying couples heat transfer, mass transfer, and phase change. Heat supplied through the shelf must reach the sublimation front without melting the ice or degrading the product. Water vapor then travels through the already dried layer and leaves the chamber, where low pressure and cold traps keep it from returning. The dried layer acts as a resistance to vapor flow, so drying rate changes as the front recedes. Open questions remain about how pore structure and formulation heterogeneity affect drying uniformity at larger scales.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and concentrates dissolved solids. Primary drying then lowers chamber pressure so ice changes directly into vapor without passing through a liquid phase. Secondary drying raises the shelf temperature to remove bound water that remains after ice sublimation. The result is a dry, porous structure that can be reconstituted later.
A typical cycle begins with freezing, which fixes the material into a solid and determines ice crystal size. Primary drying then raises heat under vacuum so ice sublimes, often near or below the collapse temperature of the formulation. Secondary drying removes bound water that remains after ice is gone, usually by gently warming the product. Each stage balances heat input against pressure to avoid melting or structural damage. Temperature probes and pressure sensors guide the transition between stages.
In practice, lyophilization is slower and more energy intensive than simple drying. Cycle times can range from hours to several days depending on load, container, and formulation. Amorphous materials may require excipients that help preserve structure during freezing and drying. The method is widely used for biological materials, pharmaceuticals, and foods where heat drying would cause unacceptable change. Open questions remain about scaling cycles between laboratory and production equipment, and this gap affects technology transfer.
Lyophilization removes water by freezing a material and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intermediate liquid state. Because the material remains frozen during primary drying, the structure often stays porous. This porous matrix can rehydrate quickly when water is added back. The low pressure also allows vapor to leave the solid matrix without boiling.
Visceral fat or abdominal fat (also known as organ fat or intra-abdominal fat) is located inside the abdominal cavity, packed between the organs (stomach, liver, intestines, kidneys, etc.). Visceral fat is different from subcutaneous fat underneath the skin, and intramuscular fat interspersed in skeletal muscles. Fat in the lower body, as in thighs and buttocks, is subcutaneous and is not consistently spaced tissue, whereas fat in the abdomen is mostly visceral and semi-fluid. Visceral fat is composed of several adipose depots, including mesenteric, epididymal white adipose tissue (EWAT), and perirenal depots. Visceral fat is often expressed in terms of its area in cm2 (VFA, visceral fat area). An excess of visceral fat is known as abdominal obesity, or "belly fat", in which the abdomen protrudes excessively. New developments such as the Body Volume Index (BVI) are specifically designed to measure abdominal volume and abdominal fat. Excess visceral fat is also linked to type 2 diabetes, insulin resistance, inflammatory diseases, and other obesity-related diseases. Likewise, the accumulation of neck fat (or cervical adipose tissue) has been shown to be associated with mortality. Several studies have suggested that visceral fat can be predicted from simple anthropometric measures, and predicts mortality more accurately than body mass index or waist circumference. Men are more likely to have fat stored in the abdomen due to sex hormone differences. Estrogen (female sex hormone) causes fat to be stored in the buttocks, thighs, and hips in women.
Creatinine (; from Ancient Greek κρέας (kréas) 'flesh') is a breakdown product of creatine phosphate from muscle and protein metabolism. It is released at a constant rate by the body (depending on muscle mass).
=== Altered substrate availability: lowered CO2 or increased O2 === Factors which influence this include the atmospheric abundance of the two gases, the supply of the gases to the site of fixation (i.e. in land plants: whether the stomata are open or closed), the length of the liquid phase (how far these gases have to diffuse through water in order to reach the reaction site). For example, when the stomata are closed to prevent water loss during drought: this limits the CO2 supply, while O2 production within the leaf will continue. In algae (and plants which photosynthesise underwater) gases have to diffuse significant distances through water, which results in a decrease in the availability of CO2 relative to O2. It has been predicted that the increase in ambient CO2 concentrations predicted over the next 100 years may lower the rate of photorespiration in most plants by around 50%. However, at temperatures higher than the photosynthetic thermal optimum, the increases in turnover rate are not translated into increased CO2 assimilation because of the decreased affinity of Rubisco for CO2.
==== Mechanical interlocking ==== The bioadhesives have the ability to diffuse and penetrate the pores and irregularities in the surface it is adhered to which forms a close interlock. This increases the contact area of the too surfaces and results in an increase in adhesive force. In bioinspired adhesive systems the application of Chitosan, was used as a bridging polymer in a 3D hydrogel network to perform topological wet adhesion. By creating strong physical bonds between synthetic materials, by creating non covalent bonds between H bonds. It was shown that Chitosan causes rapid cohesion 1000 J·m⁻² by 3 and 2000 J·m⁻² by 10 min. Chitosan diffuses and soaks which causes chitosan to move into the polyacrylamide mesh and weave themselves through. Chitosan penetrates deep as ~ 25 μm in tendon and skin after 10 min and 1h of compression respectively.
Sources: en.wikipedia.org
== History == The Inner London Education Authority was established when the Greater London Council (GLC) replaced the London County Council (LCC) as the principal local authority for London in 1965. The LCC had, in 1904, taken over from the London School Board responsibility for education in Inner London. In what was to become Outer London, education was during the first half of the twentieth century primarily administered by the relevant county councils and county boroughs, with some functions delegated to second-tier councils in the area. The Herbert Commission report in 1960 recommended the establishment of the Greater London Council. It advocated a London-wide division of educational powers between the GLC and the London boroughs. The GLC would be responsible for strategic control of schools, and the boroughs for routine management. This part of the report was rejected by the government. Councils in the future Outer London area wanted greater control over education, preventing the creation of a London-wide local education authority (LEA), and there was strong opposition from teachers and other bodies to the idea of dividing up the LCC LEA. The London Government Act 1963 therefore created the ILEA to inherit the educational responsibilities of the LCC, and gave Outer London boroughs LEA status. The ILEA was originally conceived as a provisional body whose status would be reviewed before 1970, but the Labour government made its status permanent in 1965. The ILEA did not cover the small area of North Woolwich, where the LCC had provided a secondary school.
April 10: Primary Education Law mandates a public girls' school in communes with over 500 inhabitants unless exempted by the Departmental Council. Mixed schools under exemption must be led by a male teacher, though a woman oversees girls' needlework. Communes may offer free schools. Fines or imprisonment are imposed for teachers accepting non-assigned students, except in exempted cases. History and geography become mandatory subjects.
Yearling lamb a young sheep between 12 and 24 months old Saltbush mutton a term used in Australia for the meat of mature Merinos which have been allowed to graze on atriplex plants Salt marsh lamb (Also known as 'saltmarsh lamb' or by its French name, agneau de pré-salé) The meat of sheep which graze on salt marsh in coastal estuaries that are washed by the tides and support a range of salt-tolerant grasses and herbs, such as samphire, sparta grass, sorrel and sea lavender. Depending on where the salt marsh is located, the nature of the plants may be subtly different. Salt marsh lamb has long been appreciated in France and is growing in popularity in the United Kingdom. Places where salt marsh lamb are reared in the UK include Harlech and the Gower Peninsula in Wales, the Somerset Levels, Morecambe Bay and the Solway Firth. Saltgrass lamb A type of lamb exclusive to Flinders Island (Tasmania). The pastures on the island have a relatively high salt content, leading to a flavor and texture similar to saltmarsh lamb.
For non-isotropic stresses in rigid bodies, depending on how the orientation of a surface is chosen, the same distribution of forces may have a component of positive stress along one surface normal, with a component of negative stress acting along another surface normal. The pressure is then defined as the average of the three principal stresses. The stresses in an electromagnetic field are generally non-isotropic, with the stress normal to one surface element (the normal stress) being negative, and positive for surface elements perpendicular to this. In cosmology, dark energy creates a very small yet cosmically significant amount of negative pressure, which accelerates the expansion of the universe.
office Chris Iijima (1969), legal scholar, folksinger Andrei Markovits (1969), professor of comparative politics at the University of Michigan Michel Rosenfeld (1969), constitutional law scholar Mark Rosenzweig (1969), professor of economics at Yale University Steven M. Cohen (1970), sociologist, director of Berman Jewish Policy Archive at NYU's Robert F. Wagner Graduate School of Public Service Sheldon Danziger (1970), political scientist at the University of Michigan Lennard J. Davis (1970), professor of English at the University of Illinois at Chicago, specialist in disability studies John D'Emilio (1970), professor of history and gender studies at the University of Illinois at Chicago; winner of the Bill Whitehead Award in 2013 Samuel Estreicher (1970), professor at the New York University School of Law Peter Grossman (1970), professor of economics at Butler University; columnist, The Indianapolis Star Robert A. Leonard (1970), forensic linguist at Hofstra University and former member of rock band Sha Na Na Michael P. Mezzatesta (1970), art historian, director of the Nasher Museum of Art 1987–2003 Paul Starr (1970), sociologist; co-founder of The American Prospect and winner of the 1984 Pulitzer Prize for General Nonfiction Paul Berman (1971), historian and social critic Philip Nord (1971), historian and professor at Princeton University Steven J.
Sources: en.wikipedia.org
=== Maintenance and surveillance === Ideally, wound dressings should be changed daily to promote a clean environment and allow for daily evaluation of wound progression. Highly exudative wounds and infected wounds should be monitored closely and may require more frequent dressing changes. Negative pressure wound dressings can be changed less frequently, every 2–3 days. Wound progression over time can be monitored with transparent sheet tracings or photographs, each of which produce reliable measurements of wound surface area.
== Applications == Because of the ability of acetalated dextran to degrade more rapidly in low pH environments like the phagolysosome of a macrophage or dendritic cell, it has been used as polymeric micro/nanoparticles. Acetalated dextran was originally developed as a vaccine carrier, but has been used for drug delivery, tissue engineering and infectious disease vaccine delivery. Its unique degradation rates have led to finely tuned release of therapeutic proteins and vaccine elements. Ac-DEX has also been shown the allow proteins to be stored outside the cold chain. Formation of nanoparticles with Ac-DEX can be made through standard methods like emulsion, spray drying and electrospray. Using sonication, inorganic nanoparticles have been embedded into Ac-DEX particles to for a composite material for cancer therapy."Prickly Nanoparticles against Cancer". article. Weinheim, Germany. 2017-03-09. Retrieved 2024-09-16. Also they have been used as a core material for cell membrane coating.
== Water and wastewater treatment == Microbubbles have been investigated as an aeration technology for water and wastewater treatment, where their long residence time, high specific surface area, and capacity to generate reactive oxygen species can improve gas-transfer efficiency and contaminant removal compared with conventional diffused aeration. Reviews of microbubble and nanobubble aeration have reported improvements in dissolved oxygen levels and biological oxygen demand removal in activated sludge processes when these technologies are applied in place of conventional aeration.
=== Imaging === Magnetic resonance imaging (MRI) is the preferred modality for the evaluation of back pain and visualization of bone, soft tissue, nerves and ligaments. X-rays are a less costly initial option offered to patients with a low clinical suspicion of infection or malignancy, and they are combined with laboratory studies for interpretation. Imaging is not warranted for most patients with acute back pain. Without signs and symptoms indicating a serious underlying condition, imaging does not improve clinical outcomes in these patients. Four to six weeks of treatment is appropriate before consideration of imaging studies. If a serious condition is suspected, MRI is usually most appropriate. Computed tomography is an alternative if MRI is contraindicated or unavailable. In cases of acute back pain, MRI is recommended for those with major risk factors or clinical suspicion of cancer, spinal infection or severe progressive neurological deficits. For patients with subacute to chronic back pain, MRI is recommended if minor risk factors exist for cancer, ankylosing spondylitis or vertebral compression fracture, or if significant trauma or symptomatic spinal stenosis is present. Early imaging studies during the acute phase do not improve care or prognosis. Imaging findings are not correlated with severity or outcome.
This way, it is possible to integrate any device by any manufacturer as long as they are controlled by a computer, which is often the case. Another important development in robotics which has important potential implications for laboratories is the arrival of robots that do not demand special training for their programming, like Baxter, the robot.
Sources: en.wikipedia.org
Lyophilization removes water by sublimation from a frozen material, while evaporation changes liquid water into vapor. The low-pressure freezing step avoids the liquid phase and can preserve heat-sensitive structures.
Vacuum lowers the pressure below the triple point of water, allowing ice to sublimate directly into vapor. It also helps remove water vapor from the product chamber and shortens primary drying.
Many aqueous solutions and suspensions can be freeze-dried, but some formulations collapse or do not form a stable cake. The process requires careful formulation and cycle development.
Freezing only converts liquid to solid. Lyophilization adds vacuum and controlled warming so frozen solvent sublimes, leaving a dry porous solid. The two steps are related but not interchangeable.